This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-216406, filed Jul. 17, 2000; and No. 2001-210984, filed Jul. 11, 2001, the entire contents of both of which are incorporated herein by reference.
The present invention relates to an optical lens unit, more particularly to a mechanism for adjusting the focal point of the optical lens incorporated in an optical lens unit.
Recent years have seen a remarkable advance in portable photographing devices and portable communication devices. The amount of data that a portable communication device can transmit is ever increasing. Along with this increase in transmittable data amount, there undergoes development of portable communication device, such as mobile telephones, each equipped with an image sensor. A mobile telephone with an image sensor functions not only as an audio communication device, but also as an image communication device. One of the components indispensable to photographing devices is an optical lens unit, which is assembled directly to the image sensor. In a camera system in which an image is focused through a lens, it is essential that lens position is adjusted such that lens focus point comes to the focal plane of the image sensor.
A conventional optical lens unit will be described with reference to FIG. 1, which is a sectional view of the optical lens unit.
As FIG. 1 shows, the optical lens unit 10 comprises a lens holder 11, an optical lens 12, a lens barrel 13, and a fastening ring 14. The small range focal point adjusting mechanism can be applied to adjust the small variation of focal distance in an optical lens or to adjust the flange back variation in the manufacturing process of a lens unit to the image sensor.
The lens holder 11 is a hollow cylinder. The lens holder 11 has a female screw 15 in the inner circumferential surface.
The lens barrel 13 is a hollow cylindrical component. The lens barrel 13 has a male screw 16 on the outer circumferential surface. The lens barrel 13 is held in part in the lens holder 11, with the male screw 16 in mesh with the female screw 15 of the lens holder 11. When rotated, the lens barrel 13 moves along the optical axis 1 of the optical lens unit 10.
The optical lens 12 has a collar. The collar 12 is clamped between the lens barrel 13 and the fastening ring 14. The optical lens 12 is thereby held by and secured to the lens holder 11.
A light source 2 applies-a light beam to the optical lens 12. The optical lens 12 focuses the light beam, forming an image in an image-forming plane. The lens barrel 13 may be rotated, thereby moving the optical lens 12 in the lens holder 11, along the optical axis of the optical lens unit 10. As the lens 12 is so moved, its focal point is moved or adjusted.
In the optical lens unit 10 of FIG. 1, the female screw 16 of the lens holder 13 and the female screw 16 of the lens barrel 13 constitute a mechanism for adjusting the focal point of the optical lens 12. The focal point adjusting mechanism enables each optical lens units to be adjusted after assembly. This is indispensable to achieve high precision focusing, using low cost production process of a camera module incorporating a lens unit. This eliminates the need to make accurate lens assembly. Also, optical lens may have a variation on the focal distance that differs from the design value, for the following reason.
Generally, low cost plastic optical lenses are mass-produced by means of molding. In the molding, molten resin is poured into molds and cooled therein, forming lenses, and the lenses thus formed are removed from the molds. The resin is gradually cooled down in the molds, thereby improving the characteristics of the resultant lenses. There is the trend that the resin cool down process is done in a short time in order to enhance the productivity of optical lenses. Consequently, the lenses have characteristics, including the focal distance, which may vary from the design values. To adjust the focal distance of each individual lens to a desired value, it is necessary to use the focal point adjusting mechanism described above. There are also variations of dimension in the lens collar 12, the lens holder 13, not to mention assembly positioning variation of image sensor and base substrate as well.
As described above, the female screw 15 of the lens holder 13 and the female screw 16 of the lens barrel 13 constitute the focal point adjusting mechanism in the optical lens unit 10. When the barrel 13 is rotated, the lens 12, barrel 13 and ring 14 move together. Both the holder 11 and the barrel 13 have a relatively large diameter. It is inevitably difficult to render the optical lens unit 10 smaller. Further, it is difficult to assemble the lens unit 10 to the image sensor with high precision, which constitutes the focal point adjusting mechanism. Additionally, dust may be generated as the screws 15 and 16 slide one upon the other in frictional contact. Dust, if generated, floats in the lens holder 11 through which the light beam travels from the lens 12 toward the focal point. The dust may therefore adversely influences the image formed in the image-forming plane.
An optical lens unit according to an aspect of the present invention comprises: an optical lens for focusing a light beam; a hollow cylindrical lens holder having, on an inner circumferential surface, a support section located on one side of the optical lens and supporting a circumferential part thereof; an elastic member interposed between the support section and the optical lens; and a lens fastener movable along an optical axis of the optical lens, clamping the optical lens jointly with the lens holder, contacting, at one end, the other side of the optical lens, and pushing the circumferential part thereof, thereby to deform the elastic member to adjust the position of a focal point of the optical lens.